1. Field of the Invention
The present invention relates to a propeller system for installation in aircrafts, and more particularly to an electric pitch control apparatus for a variable-pitch propeller.
2. Description of the Prior Art
A conventional pitch control mechanism for a variable-pitch propeller includes a hydraulic actuator which is operated under control of a governor to vary a pitch angle of the propeller blade. The governor is mechanically operated to detect a difference between target and actual rotational numbers of the propeller for controlling a supply amount of hydraulic fluid under pressure to the hydraulic actuator. The operation timing of the governor is manually adjusted by a pilot of the aircraft, separately from operation of an output lever for torque control of a prime engine of the aircraft. It is, therefore, difficult to properly control the pitch angle of the propeller blade in accordance with an instantaneous operational condition of the propeller.
To overcome such a difficulty, there has been proposed a pitch control apparatus which is designed to determine a target rotational number of the prime engine in response to operation of the engine output lever and to control the pitch angle of the propeller blade in such a manner as to coincide an actual rotational number of the prime engine with the target rotational number. In the case that a supply amount of hydraulic fluid under pressure to the hydraulic actuator is controlled in accordance with a difference between the actual and target rotational numbers of the prime engine, however, there will occur response delay in operation of the hydraulic actuator and the component parts of the pitch control mechanism. As a result, adjustment of the pitch angle of the propeller blade to a desired value is effected with delay of a time after operation of the engine output lever. For this reason, a hunting phenomenon in rotation of the propeller will occur particularly when the difference between the target and actual rotational numbers of the prime engine becomes less than a predetermined value, and it takes a time for coinciding the actual rotational number with the target rotational number.